QUOTE
1.Even though you can achieve more headroom on vocals sometimes you don't want to.
2.Tell(don't ask) the bands what they are using.
3."Sling" bands who don't turn up or are late for soundcheck.
4.DO NOT allow the bands to use their own soundmen.
5.You Don't always need to mic up electric guitars.
6.Try and have at least two other people to assist you with monitors,cables and unexpected happenings.
7.Don't use your backline as backup.
8.Use headphones to fine tune the mix.
9.Make sure you have a lighting fixture near the desk.
10.Take a packed lunch.
11.Have every conceivable lead at hand for even the most unlikely eventuality.
12.Take a plentiful supply of Prozac!!!
In response
1. Headroom is just that. If its there it doesn't have to be used. Its like the 5th and 6th monitor mix when a duo take to the stage.
2. Bands like to use gear they are comfortable with, but at the same time, if you're running the show you only have a limited time you should as you say have some authority.
3. Sling bands who turn up late due to them being unorganised or lazy. A band that has arrived late after spending a number of hours extra on the road due to a breakdown or bad traffic or weather will need looking after.
4. I provide PA for a handul of bands on a regular basis along with the majority of work which is last minute one off (which pays well

). A couple of these have their own sound engineer. If I were to say they cannot use this engineer they would not play and I woudln't get paid and probably woudln't work with them again. I think its a case by case thing. If they have a soundman that knows what they are doing its often BETTER to use them. If its someone who knows about faders going up and down then its best not to.
5. This is true. It's unnecessary in a small venue to do this. However to look at it another way, if you are running monitors, a mic'd up electric guitar can be fed through the monitors. It might mean the guitarist can turn his amp down, somewhat lowering the backline level (always good)
6.Agreed, although the more you have, the more you have to pay.
7.Better still don't carry a backline with you unless its required and being paid for.
8.Vital to have a pair. Whilst we can mix without them its nice to able to hear what's really going off on a particular channel.
9. Racklights and desk lights are God-sends. I hate having to carry a maglite between my teeth.
10. Food is always good.
11. And more.
12. But look back at a recent thread about working hours. and your ability to work properly and safely after a number of hours. This is even more important for working at height. working with heavy loads, driving, etc.
I'm a little concerned that you didn't have fun. At the end of the day, it is a job, but its a job we choose to do. It often pays less, is longer hours, poor hours, and there's alot of hard work to be done. We choose it over working in a shop, office or factory as we enjoy it. if you find you don't enjoy it then you have to question why you do it surely?
Or am I reading it wrong. Was it this particular gig you didn't enjoy?
Either way, welcome to the world of sound engineering

We hope you enjoy your stay.
Rob